1. Field of the Invention
This invention relates generally to sprayed instrumentation and in particular to composites used for thermal sprayed instrumentation.
2. Description of the Prior Art
As the gas temperature in turbine engines increases, improvements to existing thermal spray instrumentation are necessary to meet the challenges associated with monitoring the temperature and strain of the various engine components operating at temperatures in excess of 2200° F. (1200° C.). A thermal spray instrument can include wire instrumentation laid down within a thermal barrier coating having a bond coat and a top coat. The wire instrumentation can facilitate the measurement of direct strain and temperature inside an engine when coupled with a data acquisition system. In a typical engine test, the thermal spray instrumentation must survive at least 50 to 100 hours of thermal cycling so that sufficient data can be collected. The main failure mechanism in thermal spray instrumentation is decohesion/delamination at the top coat/bond coat interface due to oxidation of the bond coat and a mismatch in the thermal coefficient of expansion (TCE) between the top coat and the bond coat. Lei, J. F., “Protective Coats for High-Temperature Strain Gages”, NASA Lewis, Tech Briefs, September 1993; Gregory, O. J., “Flame Spray Strain Gages with Improved Durability and Lifetimes”, Annual Technical Report for NASA Aerospace and Power Program NRA-01-GRC-02, October 2002; Roesch, E., “Improved Strain Gage for High Temperature Test Engine Application” Eighth Hostile Environmental Conference, Dearborn, Mich., October 1995; Wachtman, J. B. et al., “Ceramic Films and Coatings”, Noyes Publications, Westwood, N.J., 1993; Niska, H. et al., “Chemical Vapor Deposition of Alpha Aluminum Oxide for High Temperature Aerospace Sensors”, Journal of Vacuum Science and Technology, 4 (2000), 1653-1659; and Trottier, C. M. et al., “Dielectric Stability of Native Oxides formed on NiCrAlY-Coated Substrates”, Thin Solid Films, 24 (1992), 254-260.
A need exists, therefore, to improve fatigue life of the sprayed coatings used to imbed strain gages and thermocouples.